This study proposes an improved method for subsurface detection of neurovascular structures and their diameter and depth prediction as crucial feedback to neurosurgeons to prevent critical damage. The method relies on frequency-domain near infrared spectroscopy and machine learning algorithms based on numerical modeling data. The tasks solved include: analyzing the impact of the technical implementation of the spectrometer, forming effective feature vectors for classification and regression, selecting algorithms, developing training methods, and experimentally testing the results. Variational autoencoder-based algorithms demonstrate superior performance in classification and strong results in regression. A key advantage of these algorithms is their ability to train on unlabeled data while preserving the physical meaning of the latent space due to the applied custom constraint. It is essential that the light detectors of the spectrometers have a high internal gain. Experimental tests confirm the feasibility of partial training on simulated data.

BACKGROUND: Time-resolved spectrophotometry enables the contact probing of biological tissues at a depth of two millimeters to several centimeters, with a spatial resolution of one to five millimeters. This technique provides a quantitative assessment of optical parameters, concentrations of main chromophores, identification of tissue type and inclusions in the volume, which is relevant for intraoperative diagnostics [1–3]. The variability of optical properties during probe squeezing necessitates the implementation of force control of squeezing, which, like positioning, is used in robotic surgery and diagnostics [4–11]. A combined mechanical and spectrophotometric approach holds promise in this regard. However, further research is required concerning spectrophotometer setup, the development of test objects, and the determination of the possibilities of positioning-force-controlled spectrophotometry for the identification of tissues and inclusions. Development of approaches to active positional force control to study the functionality of spectrophotometry in identifying tissue structures. MATERIALS AND METHODS: An experimental bench was constructed based on a two-wavelength spectrophotometer with OxiplexTS frequency approach (ISS Inc., USA). This bench allows for the position control of the optical probe using a robotic mini-manipulator (U-Arm, China). Additionally, a software program was developed to record the pressing force of the fabricated probe in a customized nozzle for the manipulator. Finally, an algorithm was proposed for processing experimental data to estimate biomechanical, optical, and physiological parameters of the tissue. A single healthy subject participated in the experimental study. Measurements were conducted on the dorsal and ventral surfaces of the forearm and on the palmar surface of the hypotenar. RESULTS: The quantitative assessment of elastic properties of biological tissue can be achieved through the use of force-displacement data. The simultaneous registration of optical parameters, concentrations of hemoglobin fractions in a unit of the investigated volume, and tissue saturation in the dynamics of probe pressing allows for the estimation of microcirculatory blood flow, the revelation of the presence and type of large vessels. The standard silicone test objects used for spectrophotometer calibration do not align with the mechanical properties of biological tissues. Given the diminutive dimensions of the optical probe, this discrepancy introduces an additional degree of uncertainty in the quantitative assessment of tissue properties. CONCLUSIONS: The addition of active force control and automated positioning of the optical probe during spectrophotometry enhances its functional capabilities for identifying tissue structures and expands its applications in robotic pre-, intra- and post-operative diagnostics. For further studies on a larger number of tissues, tissue structures and mimicking tissue test objects, an improvement of the experimental bench is required: increase of the sensitivity of the force sensor, smoothness and discreteness of the motion during positioning, e.g. by replacing the mini manipulator by a collaborative robot. The improvement of the software part implies the implementation of synchronization with OxiplexTS through its input interface module, writing a program for automatic surface scanning.

ABSTRACTThrough numerical modeling, it has been determined that near infrared spectroscopy with a frequency domain approach can detect neurovascular structures with diameters from 0.5 mm at source‐detector distances of 5–8 mm, depending on optical parameters and technical implementation of the method. Among the five classical machine learning methods considered, quadratic discriminant analysis is the most effective for detection. Furthermore, it has been demonstrated that the use of a photomultiplier tube and the registration of both amplitude and phase signal components exhibit the highest sensitivity. Spectroscopy can rival modern ultrasound for detecting arterial vessels. A cross‐shaped probe configuration improves sensitivity, and the ratio of reduced scattering coefficient values at different wavelengths is informative for blood‐filled vessel detection. These findings are consistent with and significantly extend previous experimental in vivo and in situ studies and could be valuable for intraoperative diagnostic tasks, particularly in neurosurgery.

The advantages of near infrared spectroscopy determine the wide possibilities of its application in neurology. The method can be used together with other neuroimaging methods (PET, MRI/fMRI) as a part of neural network or classical machine learning model for the diagnosis of dementia and determination of its type. It is possible to use the NIRS system for multiple, repeated, patient-friendly telemedical control of the dynamics of the patient’s condition in a local medical center or while a home visit of a specialist for timely correction of provided treatment. This paper highlights the main aspects of the design of a system for personalized NIRS diagnostics and telemedical control of the patient’s condition in neurology and presents the development of a prototype of NIRS measuring transducer, according to medical and technical requirements. The advantages of the proposed electrical scheme of the measuring transducer are a compact design due to the use of a multi-frequency approach and the possibility to register the concentration of three chromophores such as oxy-, deoxyhemoglobin, oxidized cytochrome-c-oxidase which allows to reduce the number of unknown variables in the regression multimodal MRI-NIRS model for simultaneous assessment of cerebral blood flow velocity and oxygen consumption rate of brain tissues.

This article describes a sapphire cryoprobe as a promising solution to the significant problem of modern cryosurgery that is the monitoring of tissue freezing. This probe consists of a sapphire rod manufactured by the edge-defined film-fed growth technique from Al2O3 melt and optical fibers accommodated inside the rod and connected to the source and the detector. The probe's design enables detection of spatially resolved diffuse reflected intensities of tissue optical response, which are used for the estimation of tissue freezing depth. The current type of the 12.5-mm diameter sapphire probe cooled down by the liquid nitrogen assumes a superficial cryoablation. The experimental test made by using a gelatin-intralipid tissue phantom shows the feasibility of such concept, revealing the capabilities of monitoring the freezing depth up to 10 mm by the particular instrumentation realization of the probe. This justifies a potential of sapphire-based instruments aided by optical diagnosis in modern cryosurgery. [GRAPHICS]

The task of monitoring the condition of the tissue during its cryodestruction is extremely relevant for cryosurgery. Previously, the concept of a sapphire cryoprobe was proposed, which makes it possible to detect diffusely scattered light from a tissue during an ice ball formation. This probe combines the advantages of sapphire as a promising material for cryosurgery, as well as the possibility of assessing the depth of tissue freezing in the contact area. The use of several light source channels inside the applicator, spaced at different distances from the detector channel, makes it possible to analyze the scattering properties of the medium using the methods of diffusion theory. In this paper, we consider the influence of the position and number of analyzed source channels on the signals recorded by the detector channel and the determined effective scattering coefficient of a two-component medium consisting of an iceball and unfrozen tissue. Differences in the scattering coefficient obtained for various channel configurations are shown, as well as the advantages of analyzing a large number of channels to describe the effective properties of the medium with a complex iceball boundary.

Modern surgical practice is supported by medical devices and instrumentation at the preoperative, intraoperative and postoperative stages. However, there is a problem of local intraoperative navigation with quantitative assessment and visualization of the structural features of biological tissues directly under the surgical instrument at the time of dissection. For solving this problem and improving the quality of surgical operations, there is a promising method called time resolved near infrared spectroscopy (TR NIRS). It provides simultaneous registration of optical and physiological parameters of the investigated tissue volume locally. The in vivo experimental study was carried out using the TR NIRS method. A vector of quantitative parameters was formed for estimation of the features of the vascular bed in the probed tissue volume. The obtained results are applicable to the development of devices for optical intraoperative diagnostics.

The issues of objectivizing the work of sensory systems, human perception of external stimuli and the presence of a reaction are relevant today. Objective control is in demand in the Paralympic and professional selection, in pediatrics and neurology. For this task, electrophysiological methods are currently used to estimate evoked neural activity in the cerebral cortex. The control of metabolism and hemodynamics in the area of neuronal activation due to neurovascular conjugation is carried out by the methods of positron emission and magnetic resonance imaging. In this case, the near infrared spectroscopy (NIRS) method is relevant and promising, but it has limitations in its use on the scalp with hair. In this paper, a specifically designed optical probe and its positioning are experimentally investigated by the frequency domain and continuous wave NIRS methods.

SIGNIFICANCE:Uncontrolled cryoablation of tissues is a strong reason limiting the wide application of cryosurgery and cryotherapy due to the certain risks of unpredicted damaging of healthy tissues. The existing guiding techniques are unable to be applied in situ or provide insufficient spatial resolution. Terahertz (THz) pulsed spectroscopy (TPS) based on sensitivity of THz time-domain signal to changes of tissue properties caused by freezing could form the basis of an instrument for observation of the ice ball formation.AIM:The ability of TPS for in situ monitoring of tissue freezing depth is studied experimentally.APPROACH:A THz pulsed spectrometer operated in reflection mode and equipped with a cooled sample holder and ex vivo samples of bovine visceral adipose tissue is applied. Signal spectrograms are used to analyze the changes of THz time-domain signals caused by the interface between frozen and unfrozen tissue parts.RESULTS:Experimental observation of TPS signals reflected from freezing tissue demonstrates the feasibility of TPS to detect ice ball formation up to 657-μm depth.CONCLUSIONS:TPS could become the promising instrument for in situ control of cryoablation, enabling observation of the freezing front propagation, which could find applications in various fields of oncology, regenerative medicine, and THz biophotonics.

Currently, the main aims of modern surgery are to minimize intraoperative damages and increase the effectiveness of postsurgical recovery. This is important for the automatized intraoperative diagnostics to have quantitative criteria based on knowledge of the optical properties of biological tissues and the mechanisms of interaction of optical radiation with biological tissues. Thus, due to measurements of the biotissue optical properties, the structure and composition of this biotissue can be determined and vice versa. The tasks of hardware and software development for in vitro and in situ laboratory diagnostics of the composition, structure and optical properties of biological tissues using a single methodological and metrological basis and the creation of an appropriate database are relevant.

The optical properties of the central nervous system components, such as gray and white matter, medulla oblongata, cerebellum and spinal cord, were studied in animal samples in vitro. Contact measurements were carried out by spectroscopy at two wavelengths of the red and near-infrared ranges in the backscattering mode. Non-contact measurements were conducted by the method of wideband spectrophotometry of the visible range in the reflection mode. The obtained quantitative narrow-spectral values of the absorption and reduced scattering coefficients of tissue samples and the relative results of the broadband measurements were analyzed. The received results are applicable to develop criteria in the tasks of automatized detection and identification of structural heterogeneities in the tissue volume for cases of surgical resection and real-time recognition of brain tissues abnormalities.

The applicability of the spectrophotometric method with phase-modulation mode for detection and recognition of large blood vessels in the volume of biotissue in situ was investigated. The results of experimental researches revealed distinctive optical and dynamic characteristics inherent in the types of vascular structures. The criteria of recognition of blood vessels in the volume of biotissue due to the optical properties of blood and slow fluctuations in hemodynamics was obtained.

One of the important tendencies of current clinical audiology is objectivization of hearing assessment. The presence of sensory perception is determined by neuronal activation of a certain area of the cerebral cortex caused by appropriate stimuli. It describes the connection of all elements of a sensor system and the performance of its main function. Hearing assessment objectivization can be provided by monitoring or operating control of electrophysiological, hemodynamic and/or metabolic parameters of the auditory cortex. Among possible direct and indirect methods of the control of the induced cerebral activity such as electroencephalography, rheoencephalography, functional magnetic resonance tomography, and positron emission tomography, the spectrophotometric method is the most appropriate one for the purpose in view. In this research, an analysis of literature data and results of preliminary experimental studies are presented. The obtained results allow us to reveal the method limitations, to formulate medical and technical requirements for development of hardware and software of the diagnostic device for objectivization of auditory detection control, and confirm the efficiency of spectrophotometric method, well known as NIRS.

Using non-invasive near infrared spectroscopy fast changes in the range of ms in the optical properties of neurons during brain activity have been described. Since the signal is small, the system to detect it has to be highly noise optimized. We used a frequency-domain tissue oximeter, whose laser diodes were modulated at 110 MHz and the amplitude (AC), mean intensity (DC) and phase (phi) of the modulated optical signal was measured at 96 Hz sample rate. In two volunteers, 36 and 37 years old, the probe consisting of 4 crossed source detector pairs was placed above the motor cortex (C3 position), contralateral to the hand performing the tapping exercise. The tapping frequency was set at 2.5 times the heart rate of the subject to avoid the influence of harmonics on the signal. An electronic device recorded the tapping movement. Control-data were obtained from a solid medium of approximately the same optical properties as the human head. To reduce physiological noise the arterial pulsatility was removed using an adaptive filter, the data was detrended by a high pass filter and a cross correlation function between the optical data and the tapping signal was calculated. The instrumental noise of the control data was very low (AC mean 0.0015% +/- SD 0.00092%, DC 0.00037% +/- 0.00023% and phi 0.00083 degrees +/- 0.00042 degrees). On the head the noise level was AC 0.0042% +/- 0.0031%, DC 0.0021% +/- 0.0012% and phi 0.0020 degrees +/- 0.0017 degrees. In 14 DC, 5 AC and 0 phi out of 30 locations a fast signal was detected, which was higher (p<0.001) than the noise level. This signal disappeared during non-tapping periods. With the signal to noise ratio that we have achieved single subject measurements become feasible.

Absolute optical values for the human adult brain are difficult to measure due to the layered structure of head. We used long-range multi-distance frequency-domain near-infrared spectroscopy (NIRS) to measure absolute optical values of each tissue layer in the human head. We determined baseline optical values for the forehead in 30 adults (age range 21 to 50). We found that tissue oxygenation was relatively narrowly distributed (STD~3%) within the subject group, whereas hemoglobin concentrations and optical parameters had a relatively broader distribution. In addition, the distance dependence of optical and physiological parameters showed the layered structure of the human head. These measurements allowed determination of absolute optical properties in each layer of the adult head.

With a low-noise frequency-domain near-infrared-spectroscopy instrument and highly effective filtering and extraction algorithms we detected functional fast signals, which are related to brain activity in the visual and motor cortex.